The present invention relates to a method and apparatus for orienting a feeler of an apparatus for testing the tooth flank profile and the flank lines (pitch of the helix) of gear wheels with respect to their axis of rotation, wherein the feeler is movable at a tangent to the gear wheel (X direction) as well as at right angles thereto (Y direction) along incremental travel transducers. The feeler is inserted in succession, at two adjacent positions, into a gap element located on the gear wheel until the feeler head contacts both sides of the gap flanks, and from the X and Y values thus ascertained at the travel transducers, with the aid of the pivot angle defined by the two positions, the location of the point of intersection of the wheel axis with the measuring plane is ascertained.
This method is known from German Pat. No. 33 20 983, where it is explained in detail in conjunction with FIG. 10. According to this description, as a substitute for the theretofore necessary orientation of the center point with the aid of a calibration device placed at the center of rotation of the gear wheel, or with the aid of an alignment device, an orientation feeler is used the head of which is a ball manufactured with high precision adapted to the modulus of the particular gear wheel to be tested. The center point orientation of the testing apparatus is performed in that the orientation feeler is moved in succession into two adjacent tooth gaps, and from the values measured in the X and Y direction in combination with the pivot angle between the two tooth gaps approached, the coordinates for the point on the wheel axis that is located in the corresponding measuring plane are ascertained by means of a calculator connected to the testing apparatus.
A disadvantage of the known type of method is that different tooth gaps are used for the orientation of the testing apparatus, and these tooth gaps likewise have a different, variable amount of error originating in the gear wheel manufacture, so that these tooth gap errors of unknown magnitude become part of the orientation process and in a correspondingly unforeseeable manner lead to an incorrect location of the wheel axes, even though an exact pitch angle is used, which is an integral multiple of the pitch angle of the gear wheel and is known from the geometry of the gear wheel to be tested.
A further disadvantage is that for the orientation process, orientation feelers must be used that have feeler heads that are adapted to the modulus of the gear wheel to be tested in such a way that the feeler head, upon insertion into the particular tooth gap comes into contact in the vicinity of the pitch circle with the flanks adjoining the tooth gap. These orientation feelers are expensive to manufacture and must be kept in inventory in correspondingly great numbers. For gear wheels having large moduli, these feelers also have considerable weight, and the moving parts of the testing apparatus, in particular, as well as the means for guiding the feelers must be designed taking this weight into consideration; overall a considerably larger and more expensive testing apparatus is required. Even then, because of their weight, the orientation feelers for large moduli have an especially major effect on the accuracy of the test results, since for the testing process they have to be replaced with a measuring feeler the weight of which may be insignificant in comparison with their own weight.
A further problem arises because it is only with extreme difficulty that the testing apparatus stand, with its approximately 1.5-meter-long guide track representing the Z direction or the Z axis, can be aligned exactly parallel to the axis of the gear wheel to be tested. Any deviation from this parallelism dictates an incorrect movement of the measuring feeler along the tooth flank profile and along the flank lines. This falsifies the gear wheel testing result, which given the accuracy presently attained in gear technology is on the order of magnitude of the measuring accuracy of the test equipment and therefore cannot be ignored.
All the above-described problems arise particularly in connection with portable test equipment, which on the one hand is intended to be lightweight and small so that it is readily portable, but on the other hand should not be inferior in its accuracy to a stationary measuring machine; yet it is highly desirable to avoid using stationary measuring equipment, so that the gear wheel that is to be tested will not need to be rechucked repeatedly, for instance during manufacture.